This invention relates to electrodes and to discharge lamps including electrodes.
Discharge lamps have two electrodes spaced from one another within a sealed envelope containing a discharge gas, or mixture of gases, at reduced pressure. When a sufficient voltage is applied between the two electrodes, discharge is produced within the gas, causing radiation. Usually, the radiation is predominantly in the UV or VUV range and, where visible light is needed, the envelope is coated with a phosphor material which fluoresces under UV irradiation to produce visible light.
The electrodes can be heated so that electrons are emitted from the cathode by primary emission. By contrast, with cold-cathode electrodes, ion bombardment of the cathode causes the secondary emission of electrons. Although hot-cathode lamps have a greater electrical efficiency, cold-cathode lamps have the advantage of a longer electrode life. An example of a cold-cathode lamp is described in, for example, GB2244855. Because of the relatively low electrical efficiency of cold-cathode lamps, anything that can be done to increase the production of electrons from the cathode is particularly important to the performance of the lamp.